1. Field of the Invention
The present invention relates to a spring-operated mechanism and more particularly to a spring-operated mechanism for actuating a switch gear, etc. although not limited thereto.
2. Description of the Prior Art
As the voltage and capacity in electric transmission and substation systems have increased, the switch gears have also tended to become larger, requiring an operating apparatus having a large output to drive the switch gears. Hitherto, for operating apparatus having large output, fluid operating systems such as pneumatic or hydraulic operating systems have been most common and motor-driven spring-operated systems have also been utilized for relatively small outputs.
However, a fluid operating system is inferior to a motor-driven spring-operated system from the standpoint of maintenance. For example, the former has such practical problems as the maintenance, inspection, etc. of a compressor in a pneumatic system, or lubricant leakage at connections of the piping, etc. in a hydraulic system.
As a motor-driven spring-operated system, one using a toggle joint has been hitherto widely used. Examples of principal elements and the operational principle thereof are schematically indicated in FIGS. 1 and 2, respectively. Now the features of a conventional motor-driven spring-operated apparatus utilizing a toggle joint will be explained below in reference to FIGS. 1 and 2.
The operational principle is shown in FIGS. 2A-2D as follows:
(i) Upon receiving a demand for operation, a motor (not shown) begins to rotate, and the torque is transmitted to a motor lever 1 through a reduction gear (not shown);
(ii) As motor lever 1 comes into contact with one of projections 2a of a spring lever 2 as shown in FIG. 2A, a spring 5 now being at a point of maximum elongation is gradually compressed by the torque of motor lever 1 to store energy therein and reaches a point of maximum compression as shown in FIG. 2B, whereby spring 5 is disposed within a spring casing pivotally mounted to a stationary member through pivots 5a in parallel with an output shaft 4. Another projection 2b of spring lever 2 abuts against an output shaft lever 3 when spring 5 for the first time reaches the point of maximum compression;
(iii) After reaching the point of maximum compression, spring 5 begins to release the stored energy to accelerate output shaft lever 3 through spring lever 2; and
(iv) When spring 5 again reaches the point of maximum elongation (in a position such that the inclination of spring 5 with respect to the vertical axis is just opposite that at the initiation of the operation.) the operation is completed as shown in FIG. 2C.
The reverse operation takes place similarly starting from the state shown in FIG. 2D by repeating the operations described above in the rearward direction.
Thus it will be appreciated that a spring-operated system of the toggle joint type has a simple operational principle, has few components, and thus exhibits superiority from the viewpoint of economy. In general, in switch gears, in particular in one provided with the ability to break an electric current, in order to obtain a sufficient initial separation speed, a large amount of energy is required at the initial phase of the operation. However, with a spring-operated system of the toggle joint type shown in FIGS. 1 and 2, since the released energy of spring 5 at the initial phase of the operation corresponding to the rotation of output shaft 4 for a predetermined angle is less than that during its operation, it is difficult to obtain a sufficient initial separation speed. In order to obviate such a difficulty it is conceivable that the maximum compressive load of the toggle joint spring can be set higher. However, in this case, it is necessary to absorb the excess energy accumulated in the moving parts of the switch gear at the time of the completion of the operation by the use of a damping means etc., and new problems occur such as increasing oscillations of the system at the completion of the operation due to impact force.
In order to remedy the difficulties inherent to the conventional spring-operated mechanisms as discussed above, Japanese Patent Publication No. 46609/1980 (filed on Aug. 15, 1975, claiming the priority of West German Patent Application No. P2439837.6 filed on Aug. 16, 1974, by Siemens A.G., entitled "A Snap Type Driving Apparatus for a Switch Gear", published on Nov. 25, 1980) discloses a mechanism wherein the parts participating in closing or opening the switch gear are disposed in a concentric manner so as to be rotatable, and further both of the parts are provided with concave portions so as to be engageable by an engaging pin connected to the energy storing spring.
Further, Japanese Laid-Open Patent Publication No. 15 9511/1980 (filed on May 31, 1979 by Tokyo Shibaura Denki Co., Ltd., entitled "A Motor Drive Spring-Operated Apparatus", laid-open on Dec. 11, 1980) discloses a mechanism wherein a crank pin connected to and driven by an electric motor is adapted to rotate a rotational shaft by a link engaging the crank pin through a slot and a lever pivoted to the link and connected to the shaft so that the torque of the electric motor causes a spring to store energy by means of the rotational shaft.
However, none of them teach or suggest the use of cam means in a spring-operated mechanism in order to make the spring release the major part of the stored energy at the initial phase of the operation of the mechanism as in the present invention.